This invention relates to monitoring liquid level in tanks, and more particularly to a system and method for manually determining and electronically indicating a liquid level condition within a tank.
The determination of liquid level, such as the level of liquefied petroleum (LP) gas, propane, butane, and so on, in transportable and stationary storage tanks is often inconvenient for vehicle operators, will-call status customers and others where a mechanical gauge head and sending unit are installed in the tank. Such customers must visually read the gauge head to determine the liquid level condition of the tank, then call a fuel supply company for tank refill. For some portable tanks, such as those used to power forklifts, generators, and other equipment, the operator is usually not in a position to constantly monitor the fuel level since the gauge head is out of the operator's view. Accordingly, the equipment can run out of fuel at a location remote from the replacement tank, causing equipment downtime and loss of revenue, power, and other conditions until the empty tank can be replaced.
For stationary tanks, located at a place of residence or business for example, a person must exit the building, approach the tank and move a protective cover located over the gauge head and other fittings in order to ascertain whether or not a fuel supply company should be contacted for refilling the tank. Consequently, many stationary tanks also run out of fuel at the most inconvenient times, such as during heating, cooking, bathing, and so on. However, such inconveniences can potentially lead to more serious consequences, such as frozen pipes during winter conditions and the attendant damage and repair costs, health degradation when exposed to low temperature conditions, and so on. The difficulty in ascertaining fuel level within the tank is exacerbated when access to the gauge head is not possible for numerous reasons, such as the location of the gauge head, physical limitations of the user, and so on.
Portable and permanently installed storage tanks for pressurized fuel and other liquids, such as liquefied petroleum gas (LPG), propane, butane, and so on, typically include a fuel sending unit mounted at the center or end of the tank for view by an observer. The sending unit typically includes a float that rides on the surface of the liquid. The float is connected to a pivoting float arm which is in turn connected to the lower end of a driven shaft that rotates about its axis in response to float movement. A drive magnet is typically located at the upper end of the driven shaft that magnetically couples with a driven magnet inside the gauge head, which is associated with an indicator and gauge plate with scale markings thereon, so that rotational movement of the drive magnet in response to float movement induces the driven magnet to rotate a proportional amount and rotate the indicator across the scale, to thereby display a liquid level condition of the tank to an observer. One such device for determining liquid level within LPG or fuel oil tanks is disclosed in U.S. Pat. No. 6,041,650 to Swindler, et al., and includes a sensing probe having a movable float arm coupled by gears to the lower end of a rotatable drive shaft. A magnet is mounted to the upper end of the shaft and extends into a passage of a gauge head for magnetic coupling with a level indicating dial. A change in liquid level within the tank causes movement of the float arm and thus rotation of the indicating dial with respect to a stationary gauge plate with liquid level indicia printed thereon, to thereby show the amount of liquid within the tank. These types of liquid level gauges must be manually accessed and visually observed to determine the position of the indicating dial with respect to the gauge plate, and is often inconvenient to do so, as discussed above.
In order to facilitate the reading of liquid level, and due to the number of portable and stationary tanks with pre-existing sending units having a magnet at the top of a rotatable drive shaft inside the tank, a liquid level gauge, which allows both manual and electronic determination of the liquid level within the tank, is disclosed in U.S. Pat. No. 6,564,632 to Ross, Jr., the disclosure of which is hereby incorporated by reference. This patent discloses a gauge head for mounting to a tank and a dial assembly for mounting to the gauge head. The dial assembly includes a base, which is in turn connected to the gauge head. A magnetically-driven indicating dial, or pointer magnet, is rotatably mounted on the base above a stationary gauge plate also mounted on the base. The gauge plate includes scale indicia around its periphery relating to liquid level in the tank. The relative position of the magnetically-driven indicating dial and the gauge plate can be viewed by a user for manually determining liquid level within the tank. This gauge also enables electronic determination of the liquid level by the provision of a circular pointer magnet with a variable thickness. The pointer magnet rotates in response to the rotation of one or more tank magnets, as disclosed in the Swindler, et al. patent referenced above. The variable thickness of the pointer magnet creates a linearly variable magnetic flux around the periphery of the magnet. A transparent lens or cover is connected to the base for enclosing and protecting the components of the dial assembly. The transparent nature of the cover allows a user to view the indicating dial and gauge plate to visually ascertain the liquid level. A channel is formed in the cover for receiving a removable magnetic detector with a single Hall-effect sensor. The channel is located at a position to ensure that the pointer magnet and the gauge plate with liquid level indicia are not obfuscated, thereby allowing the simultaneous visual observation of the liquid level and electronic determination thereof by electronically sensing a change in the magnetic flux of the pointer magnet, and thus its angular position with respect to the magnetic detector. The angular position of the pointer magnet is indicative of liquid level in the tank. The electronic signal produced by the magnetic detector can be sent to a remote location for viewing by a user or further processing, notifying a distributor of LPG or the like of the liquid level condition within the tank for scheduling delivery of LPG, and so on.
Although the above-described system is adequate for manually and electronically indicating liquid level, the specially shaped pointer magnet with variable thickness is a specialty item that is relatively expensive to manufacture when compared to ordinary magnets, requires calibration, and thus increases manufacturing time and costs, thereby increasing the overall cost of the gauge head.
It would therefore be desirous to overcome one or more disadvantages of liquid level gauges associated with storage tanks as discussed above.